Why Not Just Give Each Champ Their Own Store?
When the winds of change begin pushing a champ toward what was previously a niche build, it tends to get crushed pretty quick. It's no secret that only a select few champions are allowed to have multiple build paths, and even then if the 'wrong build' gets too strong it'll get destroyed. AP ratios get removed. AD ratios get removed. Ratios get chopped off at the knees to discourage building this or that item.
So... why even beat around the bush over it?
What if every champion had their own custom store with, say, twelve to eighteen items in it? Those items are each unique to that champion and play to their strengths (or weaknesses). Item too strong on a given champ? Their version of it gets nerfed without ruining it for everyone else. Riot doesn't want someone to be built as an AP champ? Then don't give them access to the lion's share of AP items (if any).
Keep in mind here, better than half the items in the game on any given champ are trap options (hey there Deathcap Vayne). What does the game gain by filling it to the bursting point with false choices?
A terrible idea, probably, but I'm curious to see what others think.